This invention relates in general to fuser for a reproduction apparatus, and more particularly to a mechanism for pressure loading of a reproduction apparatus fuser.
In typical commercial reproduction apparatus (electrographic copier/duplicators, printers, or the like), a latent image charge pattern is formed on a uniformly charged charge-retentive or photoconductive member having dielectric characteristics (hereinafter referred to as the dielectric support member). Pigmented marking particles are attracted to the latent image charge pattern to develop such image on the dielectric support member. A receiver member, such as a sheet of paper, transparency or other medium, is then brought into contact with the dielectric support member, and an electric field applied to transfer the marking particle developed image to the receiver member from the dielectric support member. After transfer, the receiver member bearing the transferred image is transported away from the dielectric support member, and the image is fixed (fused) to the receiver member by heat and pressure to form a permanent reproduction thereon.
One type of fuser device for typical electrographic reproduction apparatus includes at least one heated roller, having an aluminum core and an elastomeric cover layer, and at least one pressure roller in nip relation with the heated roller. The fuser device rollers are rotated to transport a receiver member, bearing a marking particle image, through the nip between the rollers. The pigmented marking particles of the transferred image on the surface of the receiver member soften and become tacky in the heat. Under the pressure, the softened tacky marking particles attach to each other and are partially imbibed into the interstices of the fibers at the surface of the receiver member. Accordingly, upon cooling, the marking particle image is permanently fixed to the receiver member. In applying pressure to the fusing nip, the pressure must be held within a desired tolerance range in order to achieve adequate fusing without disrupting transport of the receiver member through the fuser device and without damaging the receiver member or the fuser device. Prior fuser devices have had difficulties in balancing these at-opposite requirements.
In view of the above, this invention is directed to a mechanism for applying pressure load force in a reproduction apparatus fuser device having at least one heated fuser member and a pressure member in nip relation to permanently fix a marking particle image to a receiver member. The pressure load force applying mechanism includes a load arm assembly rotatable about a fixed pivot axis to apply a pressure force to the pressure member, and a load cam selectively rotated about a drive shaft. A cam follower member is associated with the load cam, wherein a force of the load cam is applied via the cam follower member to the load arm assembly. A spring nest is formed as a part of the load arm assembly. The spring nest supports at least a heavy spring and a light spring; wherein the cam follower member, upon movement under the influence of the load cam, compresses the nested light spring and the heavy spring at different travel positions of the cam follower for varying the pressure force on the pressure member.
The invention, and its objects and advantages, will become more apparent in the detailed description of the preferred embodiment presented below.